1. Field of Art
The present invention relates generally to a process and apparatus for preparing a heat treated solid foodstuff, and more particularly it relates to a process wherein a solid food is sufficiently heated deep into the center portion thereof to be sterilized and/or cooked and then cooled without impairing the appearance and flavour thereof.
2. Prior Art
The known methods of processing solid foodstuffs to give them with good storage properties involve the technique of hermetically packing foods in containers, such as cans or flexible pouches, followed by heating to sterilize the thus packed foods. However, the aforementioned processing method has a disadvantage that the textures and shapes of packed solid foods are apt to be disintegrated due to heating which had to be continued for a long time in order to sterilize or cook the contents located at the center portions in the cans or pouches sufficiently, with attendant disadvantages that the flavours and tastes of the contained foods are deteriorated.
An aseptic filling-packing technology attracts public attention, because it provides economical merits and ensures safety in operations and high production quality. In the aseptic filling-packing technology, a foodstuff is presterilized at a high temperature for a short period of time before it is packed in a container. However, up to date, the aforementioned aseptic filling-packing technology has been applied only for the preparation of liquid foodstuffs, such as milk and juice; and there is found extremely few cases where the aseptic filling-packing is successfully applied for commercial productions of solid foodstuffs or liquid foodstuffs containing solid ingredients.
This is because a solid food is hardly sterilized deep into the center portion thereof while preserving integrity or shape thereof.
A known process for the sterilization of a food containing solid ingredients is a continuous sterilization process utilizing a scraped surface heat exchanger. However, since the conditions for sterilization in this known process are set to sterilize the solid ingredients contained therein sufficiently, there arises a problem that the liquid composition of the food, such as sauce, is often heated excessively to result in deterioration in quality of the liquid composition.
Moreover, the residence time in the heat exchanger or a holding tube of the solid ingredients contained in the processed food varies significantly, leading to the result that the solid ingredients are not evenly sterilized. In order to effect uniform and full sterilization of solid ingredients thereby to ensure sterility of the finished product, the process must be designed to have an extremely large tolerance or safety factor.
With the aim of excluding various disadvantages of the conventional processes, as described above, there has been developed a system for filling and packing a food consisting of a solid ingredient and a sauce composition, which comprises the step of sterilizing solely the solid ingredient in a batch type container, the step of sterilizing and then cooling the sauce composition separately by means of a heat exchanger, and the step of aseptically mixing the sterilized solid ingredient with the separately sterilized sauce composition. Such a process is disclosed, for example, in British Pat. Nos. 1,575,069 and 1,575,070.
However, since the batch type processing vessel is rotated to effect even and full sterilization of solid ingredients and to mix the solid ingredients uniformly in the sauce, in the known system described in the preceding paragraph, the solid ingredients are apt to be deformed or collapsed. Further disadvantages of the system are that the tubing and connections for feeding the sterilized sauce to the container are so complicated that it requires intricate operations and that a risk of secondary contamination is increased.